1. Field of the Invention
The present invention relates to a process for regenerating and rejuvenating additive-based catalysts.
2. Prior art
Innes et al. (U.S. Pat. No. 5,155,075) discloses a process for regenerating a coke contaminated reforming catalyst comprising platinum on a molecular sieve. The process involves contacting the catalyst with a halogen-free oxygen-containing gas at a temperature of less than 780° F. and then oxidizing the coke. The catalyst is then suitable for use in the reforming process where C6–C11 paraffins, olefins and naphthenes are converted to aromatic compounds.
Additive-containing hydrotreating catalysts are known in the art. For example, European patent application 0 601 722 describes hydrotreating catalysts comprising a gamma-alumina support impregnated with a Group VIB metal component, a Group VII metal component, and an organic additive which is at least one compound selected from the group of compounds comprising at least two hydroxyl groups and 2–10 carbon atoms, and the (poly)ethers of these compounds.
WO 96/41848 describes a process for preparing an additive-containing catalyst in which the additive mentioned above is incorporated into a finished catalyst composition. That is, a catalyst composition comprising hydrogenation metal components in the oxidic form, brought into that form by calcination, is contacted with the specified additive.
Japanese patent application 04-166231 describes a hydrotreating catalyst prepared by a process in which a support is impregnated with an impregnation solution comprising a Group VIB metal component, a Group VII metal component, and, optionally, a phosphorus component. The support is dried at a temperature below 200° C., contacted with a polyol, and then dried again at a temperature below 200° C. Japanese patent application 04-166233 describes an alkoxycarboxylic acid-containing catalyst prepared by substantially the same process.
Japanese patent application 06-339635 describes a hydrotreating catalyst prepared by a process in which a support is impregnated with an impregnation solution comprising an organic acid, Group VIB and Group VII hydrogenation metal components, and preferably a phosphorus component. The impregnated support is dried at a temperature below 200° C. The dried impregnated support is contacted with an organic acid or polyol, after which the thus treated support is dried at a temperature below 200° C.
Japanese patent application 06-210182 describes an additive-containing catalyst based on a boria-alumina support comprising 3–15 wt. % of boria.
Non-prepublished European patent application No. 00201039 in the name of Akzo Nobel filed on Mar. 23, 2000, describes a catalyst containing an organic compound comprising N and carbonyl.
The additive-containing catalysts of the above references all show an increased activity in the hydrotreating of hydrocarbon feeds as compared to comparable catalysts which do not contain an additive.
During the hydrotreating of hydrocarbon feeds, the activity of the catalyst decreases. This is caused, int. al., by the accumulation on the catalyst surface of carbon-containing deposits, which are generally referred to as coke. The accumulation of these deposits is detrimental to the activity of the catalyst. Therefore, a catalyst is commonly regenerated after a certain period of use by burning off the coke, which renders the catalyst suitable for reuse.
However, it has been found that in the case of additive-based catalysts, the activity of the catalyst after regeneration is not always sufficient. Even when after regeneration the catalyst is again contacted with an additive in accordance with the teachings of WO 96/41848, the activity of the resulting catalyst is not always sufficient.
There is therefore need for a process for regenerating and rejuvenating additive-based catalysts in such a manner that the activity of the resulting catalyst is restored to the level of the additive-based catalyst in its fresh state. In some cases, and preferably, the activity of the regenerated and rejuvenated catalyst may be even higher than that of the fresh additive-based catalyst. In the context of the present specification, the activity of the catalyst being restored to the level of activity of the catalyst in the fresh state means that the catalyst will have a relative volume activity of at least 90 in the process for which the catalyst is intended to be used, when the activity of the fresh catalyst is set at 100.